¡¡¡¡The reproduction quality of color image mainly depends on the level of the image and the degree of color reproduction. The order and hierarchy of images refers to the distribution of density data between light and dark and light and dark. However, the order and level are not the same concept, and the order refers to the density change of the overall light and dark contrast of the image, which is a collection composed of each step hierarchy. The hierarchy is the density level between light and dark tones, the level of which determines the color change and texture on the screen, and it is the basic unit of the composition order. Both the order and the level, they are all functions of density, they are the external manifestations of density. In the process of color printing reproduction, the reproduction of the hierarchical level becomes the reproduction of density.
¡¡¡¡We can control the ink layer density by using densitometer to guide Shanghai printing and improve printing quality. Color reproduction means that the printed matter can faithfully restore and ensure the color consistency of the same batch of products. Color is now divided into two steps: color decomposition and color synthesis. Color decomposition is to decompose the original color into three primary colors, and make each color version. Color synthesis is to use the printing plate to imprint the three original color ink on the paper or other printing materials to reproduce the original color. In order to improve the color reduction, people usually use colorimeter to judge and evaluate the color reproduction of printed matter. This paper gives a brief introduction to how to choose the measuring instrument correctly for different purposes.
¡¡¡¡1. Printing ink layer density and dot expansion.
¡¡¡¡Printing field density refers to a kind of color is printed on substrate reflection density field color piece, are the major factors affect the field density of ink pigment, link to light absorption and ink layer thickness of the ink and ink film conjunctival state, etc. In the specific production process, once the ink is determined, the density of the field is only related to the thickness of the ink layer, which indirectly reflects the thickness of the ink layer on the substrate. Therefore, the measurement and control of field density is the basis of objective evaluation of printing quality.
¡¡¡¡Density gauge measuring principle of the physical color piece is densitometer internal light source the light after color filter, irradiation on color piece on the spot, spot color piece to absorb part of the light, also part of the light reflected at the same time, by reflected light by densimeter of receivers, densimeter internal electronic components compare differences in the two luminous flux, calculate the density value, density value is a no unit quantities. There are a variety of densitometers on the market, although they are different in structure, but they are basically interlinked in principle. Densitometer structure differences will affect the density of the measurement result, that is to say, with a different manufacturer production density gauge measuring the density of the same color piece may have different values, but we can't say, a densitometer measurement is correct, and the other a densitometer measurement error. Actually, also does not have the absolute density in the field of offset printing reference, we used the recommended reference is just a range, as long as the print density values in this range, we all think the print is qualified.
¡¡¡¡Dot expansion value refers to the percentage of dot area between the dot area and the corresponding printed matter. We can also use densitometer to calculate the dot expansion value. Specific principle is as follows: density gauge field density measured first, and then measure the node density, network coverage calculated through electronic components within the density meter and the calculated results show that on the LCD, so we can calculate the dot enlargement. It is worth noting that, before measuring the density, we first need to increase the zero calibration on the white paper. In the measurement, the printed matter should be flattened to ensure that the measuring head is in close contact with the measured block to reduce the measurement error.
¡¡¡¡2. Color measurement.
¡¡¡¡In printing process we're going to have some cannot density meter is used to solve the problems, such as: computer display color calibration and measurement, the calibration of digital proofing equipment, digital proofing product evaluation evaluation field color piece and color reproduction and so on. People often use colorimeter on same batch with every piece of chromaticity measurement, and will be subject to the shade of the same color standard color piece value, measure the same batch with colored blocks Δ E color, if we control Δ E value within the prescribed scope, can guarantee the same product before and after the transfer, or the same sample of color deviation does not exceed the permitted range. In December 1993 issued by the provided in the conditions of press and publication administration of high quality products with the batch chromatism Δ E same color standard should be less than 4. During the colorimeter measurement, it is important to note that zero calibration is first raised on the "standard white board" instead of a zero alignment on the white paper. In the measurement, the printed matter should be flattened to ensure that the measuring head is in close contact with the measured block to reduce the measurement error.
¡¡¡¡There are, of course, situations where the quality of print reproduction can be objectively reflected only by the simultaneous use of densitometers and colorimeters. For example: the reproduction of grey balance. At present, the market also has the colorimeter and densitometer together as an integrated instrument. We call it a color densitometer with a polarizing mirror device, which has its unique flexibility. Its density of polarizer device can be used in measurement, the purpose is to eliminate ink layer surface reflective parts (including the mirror reflection and diffuse reflection of light), make sure the wet density measurement is dry density back later, so we use this kind of color densitometer measure the wet density values than in other density meter measure the value of the small.